dpx: perform width/height upgrade and av_image_check_size earlier to prevent segfault on malformed input

Signed-off-by: Peter Ross <pross@xvid.org>

libavcodec/dpx.c

@@ -104,6 +104,11 @@ static int decode_frame(AVCodecContext *avctx,
     buf = avpkt->data + 0x304;
     w = read32(&buf, endian);
     h = read32(&buf, endian);
+    if (av_image_check_size(w, h, 0, avctx))
+        return AVERROR(EINVAL);
+
+    if (w != avctx->width || h != avctx->height)
+        avcodec_set_dimensions(avctx, w, h);
 
     // Need to end in 0x320 to read the descriptor
     buf += 20;
@@ -182,10 +187,6 @@ static int decode_frame(AVCodecContext *avctx,
 
     if (s->picture.data[0])
         avctx->release_buffer(avctx, &s->picture);
-    if (av_image_check_size(w, h, 0, avctx))
-        return -1;
-    if (w != avctx->width || h != avctx->height)
-        avcodec_set_dimensions(avctx, w, h);
     if (avctx->get_buffer(avctx, p) < 0) {
         av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
         return -1;